As life has modernised in recent centuries, so have the places we live. Infrastructure, development and the changing nature of work have all played a hand in creating cities and urban spaces as we know them today, as well as the problems that come with them.
However, there are also developments in our approach to these areas, incorporating nature into the structures we have built. Let’s talk about the power of green walls.
What are green walls
Green walls are also known as living walls, vertical gardens or ecowalls. They’re vertical structures with different plants and greenery attached to them. They differ from facades, which refers to plants that climb the outside walls of buildings and use them for structural support (eg. ivy). Facades are rooted to the ground, whereas green walls grow in a medium that is found on the structure of the wall itself. While facades can take a long time to grow to cover a whole wall, green walls can be designed and pre-grown to cover the surface they’re intended for. They can be installed both indoors or outdoors, can range in size from just a few square feet to entire walls in atrium spaces and, on average, they have 50 plants per square metre.
While plants have been growing on walls since buildings were first erected, the idea of designed walls was first patented by Stanley Hart White, a professor of landscape architecture at the University of Illinois, in 1938. The concept didn’t take off at the time. It was popularised by Patrick Blanc, however, after he created one of the most famous green walls at the Musee du Quai Branly in Paris, sparking a revolution in sustainable architecture.
Green walls fall under the larger category of green infrastructure, which also includes green roofs and pocket parks. All of these interventions aim to bring plants to urban spaces where they’re needed. Outdoor living walls, in particular, can be vital to the future of cities and wellbeing. While inspirational and aesthetically pleasing, the addition of nature to buildings provides multiple benefits, and so far they’ve been seen on the outside of skyscrapers, hotels and large retail buildings.
Indoors green walls can often be found in lobbies, receptions areas, meeting rooms and hallways, providing plant benefits without taking up floor space. Companies tend to see them as an investment, not just for sustainability but also to improve employee wellbeing and creativity, while reducing health risks.
How are green walls constructed?
Green walls differ depending on context but are usually built with a skeletal structure with sections containing the plants and flowers that will make up the wall. Categories include:
- Panel systems: using wall panels with pre-planted plants. They can be used inside or out, in any climate, and are installed directly onto the wall of a building using a support structure.
- Felt systems: Plants are placed in felt pockets, with pipes running through the wall to keep the felt moist, allowing plants to grow.
- Tray systems: popular indoors, plants are grown off-site and inserted into the wall, offering versatility that can be used to cover large surfaces
- Trellis systems: plants grown in containers are trained to grow up a wall trellis.
- Freestanding walls: commonly used indoors and most easily changed, either by changing the location or changing the plants.
Whatever structure is chosen is attached to the wall, with a growth medium placed on to form a system (eg. soil packed into bags and placed on the wall). Plants are usually chosen based on what is native to the area, resilience, the weather conditions it needs to withstand, what it can be grown in (some plants will need soil and some don’t), air purification efficiency, and wide-ranging tolerances.
When it comes to water, most green walls are designed with an automated drip-irrigation system, maximising water use and minimising waste. Recirculation systems are the most efficient, reusing water repeatedly by pumping it from the bottom to the top until there’s none left, with the tank then refilling. When spaces have no room for tanks direct irrigation is an option, while advanced walls may use rainwater capture systems.
Most green walls usually come with a warranty that guarantees initial maintenance from the installation company, as the first few months are essential to hone irrigation and care. After that, many companies offer options to continue caring for the wall, depending on client preference. Soil needs to be maintained, drainage needs to be properly managed, and plants need to be looked after. While all of this installation and upkeep may seem expensive and fussy, the overall benefits outweigh these costs.
The benefits of green walls
Improved air quality
We all know that plants create oxygen. In urban environments, where plants may be scarce, green walls can help to improve air quality, both indoors and out. Around 25% of carbon emissions made by human activity are absorbed by plants, living walls provides more plants to do the work, filtering toxins in the air and converting carbon dioxide to oxygen.
In densely populated areas this is vital, as pollutants and aerosols become trapped in urban street canyons. Green infrastructure has huge potential to improve this air quality, as plants capture toxins, gases, aerosols and particulate matter. This includes dust particles, improving air around construction sites and busy roads. Just 1 m² of living wall extracts 2.3 kg of CO2 per annum from the air and produces 1.7 kg of oxygen, while studies show that plants and microbes found in their soil absorb harmful VOC’s and convert them into compounds which plants feed on.
Plants absorb and reflect some sunlight, which cools the air, decreasing ambient temperature significantly.
Many cities struggle with the heat-island effect, where machinery, vehicles, and buildings give off heat which gets trapped in cities, driving up temperature. These effects can also be linked to environmental racism in cities. Racist housing practices, which concentrated BIPOC into specific areas, usually pushed these communities into neighbourhoods with less cooling green space or tree shade. On a hot day, a neighbourhood with little shade can be up to 20F hotter than a more affluent and greener area in the same city.
Plants lower this temperature through a process known as evapotranspiration: where the combination of water evaporated into the atmosphere and plant transpiration reduces overall temperature. The more green infrastructure used, the more this effect takes place.
This cooling effect in warm months is also echoed by an added layer of insulation in the winter. Both of these reduce costs due to less reliance on heating/air conditioning, while also making buildings more efficient overall.
Less noise polluion
Sound reflects off flat, non-porous surfaces, so the introduction of plant walls also helps make noisy spaces quieter. Sound vibrations are absorbed by plants rather than reflected back, as plant walls absorb around 41% more noise than traditional walls.
Outdoor walls also reduce noise from traffic, building work, aircraft and other urban noise pollution. Vegetation naturally blocks high-frequency sounds while the supporting structure can help to diminish low-frequency noise. Ambient noise can be reduced 50%, by up to 8dB, bringing more peace and quiet.
Extending the life of infrastructure
Green walls also increase the longevity of built spaces. Walls are exposed to changing temperatures, UV radiation, wind, heavy rain and other elements that can cause deterioration, cracks and fissures due to expanding and contracting materials. A green wall protects the actual structure underneath from direct damage or exposure, potentially extending the life of these walls by years, making the overall building more sustainable.
Plants contain a lot of moisture, making them naturally more resistant to fires. Plant walls, in particular, are designed to remain lush and green most of the time, adding a fire-resistant layer to any building.
Green walls also reduce stormwater management for buildings, especially in older areas where stormwater combines with wastewater systems. Advanced free walls can use excess rainwater for green wall irrigation, but all green walls will absorb rainwater as a natural buffer. This delays rainwater reaching sewage systems and purifies the rainwater, plus water evaporates through the plants, helping keep overall groundwater stable and reducing flood risks.
Green walls increase the biodiversity of urban spaces by offering a variety of plants for nesting, shelter, and food for birds and insects. Most green wall installations value a variety of native plants for aesthetics and because these plants will survive in the climate they’re placed in. This broad range is perfect for animals, increasing the number and variety of animals in the areas they’re installed. Within days of installation bees and butterflies are usually spotted
Our maintenance team have observed bees collecting nectar from the flowers at the top of the Edgware Road living wall. This wall was installed to reduce the air pollution and some of the busy main road at the base of the wall is one of the major sources of air pollution in the area. But the bees don’t care why the living wall was installed. All they know is that it is there and that they can use it for their own purposes.
In association with Buglife we designed and developed our own integrated habitat boxes. They slot neatly into our living walls and provide refuge for a number of species including solitary bees, butterflies, ladybirds and lacewings. Our 1,800m2 living wall on the Veolia Energy from Waste Facility in Leeds includes 750 of these for example.
Health & wellbeing
Being outdoors inherently increases wellbeing. Extensive research has found that more access to green (and blue) space is vital for mental health. Creating more green spaces in urban environments, therefore, helps locals communities. Living walls offer a solution in even the densest, busy environments, giving people a literal and metaphorical chance to breathe.
At the same time, the cleaner air provided by green walls can also lead to fewer health problems, including decreased risk of headaches, irritated eyes, sore throats, and tiredness.
Potential power sources
The Botanic Gardens in Cambridge also hosts something known as the ‘P2P Solar Hub’. Created by researchers from Cambridge University, this hub uses a green wall system with a layer of carbon fibre, allowing electricity created by growing plants to be harnessed. This offers the potential to connect green walls with solar panels, creating self-powered sustainable buildings for diverse use all over the world, from bus stops to refugee shelters.
Where to see green walls
Many buildings can implement a green wall system, as companies exist across the world that specialise in their installation. These structures provide multiple benefits for people, planet and urban environments, and I hope we see their increased use in years to come.
In the meantime, they’re also beautiful to look at, and there are some particularly famous ones that are worth seeing if you’re passing by. If you find yourself travelling anytime soon, make sure to look out for:
- The Athenaeum Hotel, London, one of the tallest green walls in Europe
- Caixa Forum, Madrid
- Changi Airport, Singapore
- Musée du Quai Branly, Paris
- El Claustro de Sor Juana University, Mexico City
- Gardenhouse, Los Angeles
- Trussadi Café, Milan
- Les Halles, Avignon
- K11 Musea, Hong Kong
- Worth Avenue, Palm Beach, Florida